1. Field of the Invention
The present invention relates to fluid machines, that is, fluid pumps or fluid motors having parallel swash plates (throughout the specification and claims, fluid pumps and fluid motors are generally called "fluid machines").
2. Description of the Prior Art
Heretofore, nonparallel swash plate type pumps (or motors) as shown in FIG. 10 have been widely used.
The illustrated nonparallel swash plate type pump is provided with a cylindrical barrel 7 which can rotate integrally with a rotary shaft 8a within a casing 9, and in the barrel 7 are formed two cylinders 3 which communicate the opposite sides of the barrel 7 with each other.
Into openings at the opposite ends of each of these cylinders 3 are liquid-tightly inserted pistons 1a and 1b, and each cylinder 3 communicates with the inner circumference of the barrel 7 through a port 10.
Also, into the barrel 7 is inserted a valve shaft 4 which is fixedly secured to the casing 9, and slide surfaces between the valve shaft 4 and the inner circumference of the barrel 7 are maintained liquid-tight.
In this valve body 4 are formed two flow passageways 5 and 6 directed in the axial direction as shown in FIG. 11, and these flow passageways 5 and 6 respectively communicate with ports 15 and 16 opening at the outer circumference of the valve shaft 4.
In FIG. 10 and FIG. 11, the valve shaft 4 is shown as being rotated by 90.degree. so that construction of passageways 5 and 6 is easily illustrated.
These ports 15 and 16 have a sector-shaped cross-section along the outer circumference of the valve shaft 4 as shown in FIG. 11, and they are formed at such positions on the slide surface between the barrel 7 and the valve shaft 4 that they can communicate with the above-mentioned ports 10.
As the barrel 7 rotates, each above-described cylinder 3 communicates alternately with the flow passageway 5 and with the flow passageway 6.
On the other hand, on the opposite sides of the barrel 7, cams 2a and 2b having inclined surfaces 2c and 2d, respectively, are fixedly secured to the inner surfaces of the casing 9, these inclined surfaces 2c and 2d are formed symmetrically to each other with respect to a transverse plane 2e shown in FIG. 10, and the tip end portions of the pistons 1a and 1b butt against the inclined surfaces 2c and 2d, respectively. It is to be noted that the pistons 1a and 1b are pressed against the inclined surfaces 2c and 2d by biasing means (not shown), and thereby a butting condition between the tip end portions 1a and 1b and the inclined surfaces 2c and 2d can be always maintained.
Owing to the above-mentioned construction, if the rotary shaft 8a is driven in rotation by driving means (not shown), then the barrel 7 also rotates in association with the rotary shaft 8a, and hence the pistons 1a and 1b each of cylinder 3 having their tip end portions held in contact with the inclined surfaces 2c and 2b will operate so as to extend and contract as a unit.
During a suction step when the pistons 1a and 1b project outwardly toward the opposite sides of the barrel 7, the cylinder 3 communicates with the flow passageway 5 through the port 10 and the port 15, and thereby liquid such as oil is sucked from the flow passageway 5 into the cylinder 3.
On the other hand, in an exhaust step when the pistons 1a and 1b are retracted towards the inside of the barrel 7, the cylinder 3 communicates with the flow passageway 6 through the port 10 and the port 16, and thereby the above-described liquid is exhausted from the cylinder 3 to the flow passageway 6.
It is to be noted that the above-described nonparallel swash plate type pump apparatus can be used also as a hydraulic motor, because the rotary shaft 8a would be rotated by making liquid flow into the cylinder 3 through the flow passageway 5 by means of a hydraulic pump not shown.
However, in the above-described nonparallel swash plate type fluid machine, since the volumes of liquid retained within the two cylinders 3 are different from each other, the position of the center of gravity of the barrel 7 would deviate from a rotational center axis 8b. Thus since barrel 7 rotates at a very high speed when the fluid machine operates as a pump, a large vibration would occur due to the eccentricity of the center of gravity.
Hence, a parallel swash plate type fluid machine in which opposed inclined surfaces of cams are formed parallel to each other has been proposed, and in this proposed fluid machine the pair of pistons 1a and 1b shown in FIG. 10 would operate assymmetrically with respect to the plane 2e, and hence it is necessary to divide the cylinder 3 into two cylinder sections.
Then, one of the two cylinder sections would be connected to the inlet side port formed in the valve shaft, while the other cylinder section would be connected to the outlet side port, and there is a problem with respect to means for connecting the inlet side ports to each other and connecting the outlet side ports to each other within the valve shaft.